Gasket

ABSTRACT

A gasket for noting an annular space between two pipes comprises an annular elastomeric member ( 10 ) having a concave formation on at least one longitudinal end face, compression members ( 20, 22 ) adjacent the longitudinal end faces and connected via a plurality of securing means ( 30 ) adapted to urge the compression members ( 20, 22 ) together, the compression member or members ( 20, 22 ) adjacent a concave formation on the elastomeric member ( 10 ) including a corresponding convex formation. The elastomeric member ( 10 ) can also include a concave formation on at least one radial face ( 12, 14 ), in which the gasket can further include at least one (preferably elastomeric) filler member in that concave formation, on the radial ( 12, 14 ).

FIELD OF THE INVENTION

The present invention relates to a gasket for use in sealing an annularspace between two pipes.

BACKGROUND OF THE INVENTION

This is a problem which is commonly encountered in the offshore oil andgas industry. Crude oil typically emerges from undersea fields atbetween 100 and 100° C. This crude oil will include low melting pointfractions which will solidify within the pipe if the oil it allowed tocool to the temperature of the surrounding water. Therefore, it isnecessary to insulate the pipe. This is usually done by providing adouble-walled pipe structure in which an inner flow pipe carries thecrude oil and an outer sleeve pipe so as to define an annular spaceexternal to the inner flow pipe. This annular space is then filled withsuitable insulating material.

It is necessary to guard against ingress of water into the annularspace. Clearly, if water is allowed into the annular space it willconduct heat from the inner flow pipe to the outer sleeve pipe anddestroy the effectiveness of the insulation. Any such accidental waterleakages therefore need to be limited to short lengths of pipe. There istherefore a requirement for waterstop gasket to seal the annular region.Such gaskets are typically inserted at intervals of 12 m, or so. Ourearlier application published as WO 96/36831 describes a gasketcomprising an annular ring of elastomeric material with flat compressionmembers either side. The compression members are drawn together usingbolts, and this compresses the elastomeric member longitudinally. Theresulting radial expansion seals against the flow pipe and sleeve pipe.This waterstop gasket is suitable for double-walled pipe structures inwhich the annular gap is approximately 100 mm. There is a requirementfor a waterstop for use with double-walled pipe systems in which theannular gap is approximately 50 mm. In these situations, the design ofWO 96/36831 can sometimes provide insufficient sealing w hen scaled downapproximately.

SUMMARY OF THE INVENTION

The present invention therefore provides a gasket for sealing an annularspace between two pipes, comprising an annular elastomeric member havinga concave formation on at least one longitudinal end face, compressionmembers adjacent the longitudinal end faces and connected via aplurality of securing means adapted to urge the compression memberstogether, the compression member or members adjacent a concave formationon the elastomeric member including a corresponding convex formation.

Preferably, the elastomeric member is unitary, but it is possible todesign a suitable gasket in which the elastomeric member is made up ofseveral components.

The elastomeric member can also include a concave formation on at leastone radial face. In that case, the gasket can further include at leastone filler member in that concave formation, on the radial face. Thefiller member is preferably elastomeric.

The securing means preferably comprise threaded members passing throughat least one of the compression members and through the elastomericmember. These can be bolts, either passing through both compressionmembers and retained by a suitable nut, or (preferably) extending intoan internally threaded blind hole on one of the compression members.This eliminates a leakage path adjacent the bolt. Alternatively, thethreaded members can be in the form of studding, secured at one or bothends (as before) with a suitable nut.

The compression members are preferably steel.

The steel compression members can each be unitary, ie in the form of aring, or they can be divided into a plurality of individual arcuatemembers. Such division of the compression members gives rise to theadvantages set out in WO 96/36831. If the compression numbers aredivided, individual arcuate portions on either side of the elastomericmember are preferably staggered.

A more secure seal can be obtained within the narrow confines to whichthe present invention relates by ensuring that the aspect ratio of theelastomeric member when uncompressed is greater than 6 and/or that theincluded angle of the concave section thereof is less than 45°. If theaspect ration is above 10, the design can become unwieldy, so this is apreferable upper limit. Likewise, an included angle of greater than 30°is desirable. A suitable aspect ration is about 6.8 and a suitable angleis about 38°.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying Figures, in which;

FIG. 1 is a cross-section through a first embodiment of the presentinvention;

FIG. 2 is a cross-section, through a second embodiment of the presentinvention;

FIG. 3 is a cross-section through a third embodiment of the presentinvention;

FIG. 4 is a cross-section through a fourth embodiment of the presentinvention; and

FIG. 5 is a cross-section through a fifth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE EXAMPLES

Referring to FIG. 1, this shows an elastomeric member 10 which isessentially ring shaped and dimensioned to fit within the annular spacefor which it is intended. Thus, the distance between the radial innerand outer faces 12, 14 respectfully will be slightly less then thecorresponding distance in the double-walled pipe structure.

The longitudinal and faces 16, 18 are formed into a concave V-profile.Adjacent the concave V-profile are ring-shaped steel compression members20, 22, the internal faces of which are formed with a convex V-shapecorresponding to the shape of the longitudinal faces 16, 18 of theelastomeric member 10. However, the angle of the concave V-section ofthe elastomeric member 10 is slightly more acute than the angle of theconvex V-shape of the compression members 20, 22.

At intervals around the ring-shaped compression members 20, 22, athrough hole 24 is formed in the member 22, aligned with a through hole26 in the elastomeric member 10 and a blind hole 28 in the othercompression member 20. The blind hole 28 is internally threaded. A bolt30 is passed through the hole 24 in the compression member 22, throughthe hole 26 in the elastomeric member 10, and is received in the threadof the blind hole 28. Tightening of the bolt therefore urges thecompression members 20, 22 together, provided longitudinal compressionto the elastomeric member 10. This, in combination with thedifferentiation of the angles of the respective concave and convexformations, forces the radial faces 12, 14 of the elastomeric member 10outwardly. This provides a suitable seal against the flow within thepipes (not shown).

FIG. 2 shows a second embodiment-of the present invention. It isgenerally similar to FIG. 1, and therefore like reference numerals areused to denote like parts. In FIG. 2, the radial faces 12, 14 of theelastomeric member 10 are formed with corresponding concave formations.As illustrated, these are simple V-formations but this is not essentialand a more rounded profile could be provided if desired.

These concave formations impart additional flexibility to theelastomeric member 10 and thus magnify the radial movement of theelastomeric material. Thus, this design may be more suitable for stillnarrower annular gaps.

FIG. 3 shows a third embodiment of the present invention, generallysimilar to the second. In this embodiment, the elastomeric member 10 isdivided into two segments 10 a, 10 b at the narrowest point of theconcave segments of the radial faces 12, 14. Such a configuration may beeasier to manufacture and assemble.

This variation on the second embodiment could of course be appliedequally to the first embodiment.

FIG. 4 shows a fourth embodiment of the present invention, generallysimilar to the third but in which additional filler members 32, 34 areplaced in the concave spaces formed in the radial faces 12, 14. Thisarrangement will operate generally similarly to the second embodiment,with similar advantages, and could equally be applied to the secondembodiment rather than to the third as illustrated. Compression of theelastomeric members 10 a, 10 b should cause the outer filler member 34to expand in the hoop direction and be compressed against the sleevepipe. Likewise, the inner filler member 32 Will be compressed in thehoop direction and compressed against the flow pipe. Sealing between thefiller members 32, 34 and the elastomeric members 10 a, 10 b will be bylongitudinal compression along the adjacent faces, caused by thebringing together of the compression members 20, 22.

FIG. 5 show a fifth embodiment of the invention. It is generally similarto the first embodiment, and therefore correlated reference numeralshave been employed. The dimensions in the radial and longitudinaldirection have been adjusted to take account of the dimensions of theintended use, but this does not affect the principle of the device.Thus, the elastomeric member when uncompressed has an aspect ratio of6.8 and the concave V-section includes and angle of 38°. This offers amore secure seal within the narrow confines to which the presentinvention relates. In general, an aspect ratio of greater than 6 isdesirable, although if above 10 the design becomes unwieldy. Likewise,an included angle of between 45° and 30° is desirable.

This embodiment also differs in that the bolt 30 of the first embodimentis replaced with a length of threaded studding 36. This passes (asbefore) through the hole 24 in the compression member 22, through thehole 26 in the elastomeric member 10, and is received in the blind hole28. A nut 38 is provided on the free end of the studding 36, tightenableagainst the compression member 22 to bring the compression members 20,22 together.

It will thus be appreciated that the present invention offers a seal foruse in a variety of annular widths which can provide sufficient sealing.Examples generally according to the first embodiment have been testedand have withstood a water pressure of 59 bar, without leakage.

It will be appreciated that many variations can be made to theabove-described embodiments, without departing from the scope of thepresent invention. For example, the changes as between the embodimentsof FIGS. 1 to 4 could likewise be applied to the embodiment of FIG. 6.All such embodiments are intended to be encompassed by the presentapplication.

What is claimed is:
 1. A gasket for sealing an annular space between twopipes, comprising an annular elastomeric member having a concaveformation, at least one steel compression member adjacent eachlongitudinal end face connected via a plurality of threaded memberspassing through at least one of the compression members and through theelastomeric member, the threaded members being adapted to urge thecompression members together, the at least one compression memberadjacent a concave formation on the elastomeric member including acorresponding convex formation, in which the threaded members extendinto an internal threaded blind hole in one of the compression members.2. A gasket according to claim 1, in which the elastomeric member isunitary.
 3. A gasket according to claim 1, in which the elastomericmember also includes a concave formation on at least one radial face. 4.A gasket according to claim 3, which the gasket further includes atleast one filler member in the concave formation on the radial face. 5.A gasket according to claim 4, in which the filler member iselastomeric.
 6. A gasket according to claim 1, in which the threadedmembers are bolts.
 7. A gasket according to claim 1, in which thethreaded members pass through both compression members and are retainedby at least one nut.
 8. A gasket according to claim 1, in which thesteel compression members are unitary.
 9. A gasket according to claim 1,which the steel compression members are divided into a plurality ofindividual arcuate members.
 10. A gasket according to claim 9, in whichindividual arcuate portions on either side of the elastomeric member arestaggered.
 11. A gasket according to claim 1 in which the aspect ratioof the elastomeric member when uncompressed is greater than
 6. 12. Agasket according to claim 1 in which the aspect ratio of the elastomericmember when uncompressed is less than
 10. 13. A gasket according toclaim 1 in which the aspect ratio of the elastomeric member whenuncompressed is about 6.8.
 14. A gasket according to claim 1 in whichthe concave formation of the elastomeric member when uncompressedincludes an angle of less than 45°.
 15. A gasket according to claim 1 inwhich the concave formation of the elastomeric member when uncompressedincludes an angle of greater than 30°.
 16. A gasket according to claim 1in which the concave formation of the elastomeric member whenuncompressed includes an angle of about 30°.